/*******************************************************************************
 * Copyright (c) 2005, 2014 springside.github.io
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 *******************************************************************************/
package com.peak.spring.boot.tools;

import java.security.SecureRandom;
import java.util.UUID;

/**
 * 封装各种生成唯一性ID算法的工具类.
 * 
 */
public class Identities {

	private static SecureRandom random = new SecureRandom();

	private static IdWorker idWorker = new IdWorker();

	/**
	 * 封装JDK自带的UUID, 通过Random数字生成, 中间有-分割.
	 */
	public static String uuid() {
		return UUID.randomUUID().toString();
	}

	/**
	 * 封装JDK自带的UUID, 通过Random数字生成, 中间无-分割.
	 */
	public static String uuid2() {
		return UUID.randomUUID().toString().replaceAll("-", "");
	}

	/**
	 * 使用SecureRandom随机生成Long.
	 */
	public static long randomLong() {
		return Math.abs(random.nextLong());
	}

	/**
	 * 基于Base62编码的SecureRandom随机生成bytes.
	 */
	public static String randomBase62(int length) {
		byte[] randomBytes = new byte[length];
		random.nextBytes(randomBytes);
		return Encodes.encodeBase62(randomBytes);
	}

	public static Long twitterSnowflake() {
		return idWorker.nextId();
	}

	public static String twitterSnowflake(long workerId, long datacenterId) {
		return Converts.toString(idWorker.nextId(workerId, datacenterId));
	}

	private static class IdWorker {

		private long workerId;

		private long datacenterId;

		private long sequence = 0L;

		private long twepoch = 1446789857406l;

		private long workerIdBits = 5L;

		private long datacenterIdBits = 5L;

		private long maxWorkerId = -1L ^ (-1L << workerIdBits);

		private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);

		private long sequenceBits = 12L;

		private long workerIdShift = sequenceBits;

		private long datacenterIdShift = sequenceBits + workerIdBits;

		private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

		private long sequenceMask = -1L ^ (-1L << sequenceBits);

		private long lastTimestamp = -1L;

		public IdWorker() {
			this(1, 1);
		}

		public IdWorker(long workerId, long datacenterId) {
			// sanity check for workerId
			if (workerId > maxWorkerId || workerId < 0) {
				throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
			}
			if (datacenterId > maxDatacenterId || datacenterId < 0) {
				throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
			}
			this.workerId = workerId;
			this.datacenterId = datacenterId;
		}

		public synchronized long nextId(long workerId, long datacenterId) {
			long timestamp = timeGen();
			if (timestamp < lastTimestamp) {
				throw new RuntimeException(
						String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
			}
			if (lastTimestamp == timestamp) {
				sequence = (sequence + 1) & sequenceMask;
				if (sequence == 0) {
					timestamp = tilNextMillis(lastTimestamp);
				}
			} else {
				sequence = 0L;
			}
			lastTimestamp = timestamp;
			return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift)
					| sequence;
		}

		public synchronized long nextId() {
			long timestamp = timeGen();
			if (timestamp < lastTimestamp) {
				throw new RuntimeException(
						String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
			}
			if (lastTimestamp == timestamp) {
				sequence = (sequence + 1) & sequenceMask;
				if (sequence == 0) {
					timestamp = tilNextMillis(lastTimestamp);
				}
			} else {
				sequence = 0L;
			}
			lastTimestamp = timestamp;
			return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift)
					| sequence;
		}

		protected long tilNextMillis(long lastTimestamp) {
			long timestamp = timeGen();
			while (timestamp <= lastTimestamp) {
				timestamp = timeGen();
			}
			return timestamp;
		}

		protected long timeGen() {
			return System.currentTimeMillis();
		}

	}
}
